What has public health ever done for us?

I was watching an old episode of the Ben Stiller show on DVD the other night and there was an amusing sketch entitled 'B- time traveller'. Janeane Garofalo plays a character who travels to key moments in history but can never quite remember enough to be useful. She knows that Washington crosses the Delaware but doesn't know if he's attacking or retreating, she knows that Pearl Harbor is attacked but can't remember exactly which day will live in infamy. Anyway, this got me thinking about the old Mark Twain novel A Connecticut Yankee in King Arthur's Court. As you can probably guess from the title, even if you haven't read it, a 19th century American is transported back in time in the novel to medieval England. After the usual confusion he ends up applying his technological knowledge and ingenuity to modernize the society. He prints newspapers, starts industrialization and 'invents' electric fences and guns. Although the book is a satire, it is undoubtedly true that a 19th century American might have had a lot more practical technological knowledge than we do today. If you were transported back to 6th century England what technological expertise would you bring? Personally I thought I couldn't do much. I couldn't tell them how to make steel, I couldn't make an engine, or a printing press, or a weaving loom. I couldn't design or build an airplane or car and I couldn't even build a clock. In fact let's face it I probably couldn't even make fire or catch animals so I'd be at a disadvantage to the inhabitants of the 6th century. But then I realized the knowledge that I hope almost everyone has today that would be useful in the middle ages. Can you imagine what an impact you could have had on society if you just got people to wash their hands, cook their food properly, eliminate rodents and isolate their drinking water from sewage? I feel better already.